Hydrostatic vs Hydraulic drive? Re: Case 222

This message is a reply to an archived post by Tom Arnold on February 24, 2013 at 10:02:29.
The original subject was "Re: Hydrostatic vs Hydraulic drive? Re: Case 222".

4x4 Question.
What would be easier to use to make a 4x4 garden tractor? 2 hydrostatic axles or 2 hydraulic axles? It seems like it would be hard to sync up the hydrostatic axles.

As a commercially-made example, IIRC, Steiner used a single variable displacement "hydrostatic" piston pump much like a typical hydrostatic LGT, and a gerotor-type motor at each driving axle.

I would GUESS the motors were connected in series?

IMHO, using that type of pump makes things simple, and provides braking, and elimates the tendency to "run away" going down a slopevthat can be a problem with a "hydraulic drive".



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Dave,
Bob's answer is correct when it comes to how Steiner went about making their 4 wheel drive tractor but it does not apply to what I believe you are asking.

I think that you were considering using hydrostatic trans-axles from two dead lawn or garden tractors and try to figure out a way to drive them mechanically and then synchronize them as far as speed and direction is concerned. As you probably know, those trans-axles are usually belt driven by the tractor's engine because the hydro pump, drive pump and differential are all encased in a single housing. That is not how Steiner went about it. They used a single hydro pump driven by the engine and then used hoses to connect that hydro pump to the drive motors that spun each axle unit. To try and duplicate that would be difficult and probably expensive. The first thing you would need are two axle units with the correct gear ratio in the differential. Those axle units would need to be the correct width and also have the correct bolt pattern for garden tractor rims.

Then you would need two geroller motors plus the coupling needed to attach those motors to the input of each axle unit. The third component would be a suitably sized hydrostatic pump unit and those can be quite pricey, meaning in the 1000 dollar range.


A much simpler method is to find two well-used Case Lo Pro garden tractors that are in rough shape and not worth restoring. Remove the trans-axle from each tractor and you instantly have the front and rear axles for your articulated unit. Those axles have a geroller motor bolted to the side of them and the axles have a Hi and Lo Range capability to give you even greater flexibility when it comes to ground speed and wheel torque. Rims and tires come with the tractors, so that problem is essentially solved. Powering the axles is not difficult because hopefully, one tractor will have a decent engine complete with the hydraulic pump and pump mount. The final item is that of controlling the motors and the tractor can also provide that by way of the Travel/Lift valve. Of course, new hoses will be needed but the tractors will also have hydraulic reservoirs and oil coolers.

You mount the axles so that the work ports of each hydraulic motor faces the middle of the tractor so that the hose connections are kept simple. And yes, you mount them in series so that the fluid leaves one port of the Travel Valve and goes to one port on the rear motor. The other port on the rear motor goes to a port on the front motor and the other front motor port returns to the Travel Valve port beside the port you already used. Of course, you will have to make sure that both axles are spinning in the same direction but that is easy to correct. Just swap the upper hose on one motor with the lower hose. And if the vehicle does not move forward when you push the Travel Valve for forward, then swap the hose connections on the Travel Valve ports.

Bob did bring up a good point regarding "runaway". This phenomenon plagued the Case and Ingersoll tractors that were built before 1986 and so they came up with a Holding Valve Kit that was installed directly to the two ports on the drive motor. These kits show up on e-Bay for $200.00 to $250.00. Any one of the would work for your application. But a better solution would be to try and find a Lo Pro Ingersoll tractor that was made in 1986 or later because that one will have a Travel Valve with the Holding Valve feature built right into it.

You will need to make a pivot point in the middle of your 4x4 so it can be steered. The steering can be done hydraulically as well by using a small hydraulic cylinder to make the tractor bend left or right. There are several ways to control that cylinder which I will not go into here. So now, the decision is up to you. Should you decide to proceed with this project, you might want to consider becoming a member of my forum so that you can have access to a lot of information that is not easily found otherwise.
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